Whereas with earlier versions I reported being able to export to FS9 .mdl files I am now getting error messages as shown below every time I try to export.
Export to FSX .mdl files works okay for same source file.

I will take a look, maybe some changes I made for the night textures of FSX did influence the FS2004 output. As that was never the main target, I might have to write a different X file for them when more advanced features are added.

The error is related to the way the night textures are stored for FSX. For FS2004 it looks like they should be written different, else MakeMDL will fail. So this only happens for objects with night textures.

I'll see if I can write a different X file for FS2004 later. But that does not have a very high priority for me at the moment.

At the moment I am not able to convert files that contain elements made with a cylindrical shape and with 'smoothing' applied ie a fueltank. The file will convert without the'smoothing' applied but the sides of the cylinder are very apparent.
Is there a possibility that this issue can be covered in a future release.

The file I sent you did come up with an immediate error when trying to import. I was also able to remake the object in the original design program and opt not to have 'smoothing' and this file, when imported, did not have any error message and I was able to export.